Research on the application of CPS-SPWM technology in cascaded multilevel inverter

Take a cascaded multilevel inverter with four H-bridges in each phase leg for example, this paper studies the basic theories of two different carrier phase-shifted SPWM (CPS-SPWM) methods: unipolar dual-frequency CPS-SPWM and bipolar CPS-SPWM, and compares the advantages and disadvantages of these two algorithms. It also does some researches on the factors which may influence the output waveform quality obviously, such as the number of H-bridge, the amplitude modulation ratio and frequency modulation ratio, etc. The results of the simulation and analysis show that the CPS-SPWM technology has high equivalent work frequency, little switching loss and quick dynamic response speed, which means it is fit for the cascaded multilevel inverter. Meanwhile, the properties of the unipolar dual-frequency CPS-SPWM method are better than those of the bipolar CPS-SPWM method. At the same time, it needs to synthesize the detailed main circuit topology, proper amplitude modulation ratio and frequency modulation ratio to gain the optimum output waveform.